Different phase shifts

[dynaman]

Hi guys,

I have been experimenting with a home made single plane balancer. I have used an accelerometer mounted on top of a ducted fan. I use two methods for determining phase shifts between trial runs,

1. A IR sensor which index's a white marker on the fan hub. This signal is superimposed onto my CRO with the acceleromter signal.
2. A strobe light which shows position of the imbalance. This strobe basically tells me the angle where the max acceleration peaks.

Now, the part that confuses me is that when I use setup (1) I get a CLOCKWISE phase shift between the no weight and trial weight runs. However, when I use setup (2) I get an ANTI-CLOCKWISE phase shift between the no weight and trial weight runs.

Why don't I get a phase shift in the same direction?

cheers

M.

 

[dynaman]

I think I figured it out. One measures lead angle and the other lag angle.

 

[dynaman]

Electricpete,

I've been using your spreadsheet for my analysis (SinglePlaneBalGraphGood.xls). Its a great tool for learning. I'm finding that "lead angle" works and "lag angle" doesn't. When I run through the hand calc I'm finding that the Ucw plotted in the spreadsheet is in the opposite direction when using "lag angle". Did I get this wrong?

cheers

Mark.